The present invention relates generally to a wave rotor apparatus and a method of using the transient gas dynamic processes within the wave rotor to accomplish an engine topping cycle. More particularly, in one embodiment of the present invention a portion of the gases in the highest pressure portion of the wave rotor based topping cycle are routed to a port adjacent to and preceding an inlet port admitting air from the compressor. Although the present invention was developed for use with a gas turbine engine, certain applications may be outside of this field.
A wave rotor is generally thought of as a generic term and describes a class of machines utilizing transient internal fluid flow to efficiently accomplish a desired flow process. Since the 1940's wave rotors have been studied by engineers and designers, and identified as particularly adapted for use in a gas turbine engine. Performance levels of gas turbine engines are enhanced by the integration of a wave rotor based topping cycle thereon.
Presently, a considerable amount of research is directed to improving the specific power and decreasing the specific fuel consumption of gas turbine engines. One approach to obtaining these goals is to raise the compressor pressure ratio (compressor exit pressure/compressor inlet pressure), and/or increase the combustor temperature. However, several constraints have inhibited the realization of an aircraft gas turbine engine having a significantly raised compressor pressure ratios and/or combustor temperatures.
Increasing the pressure ratio causes an increased gas density that often necessitates the use of smaller passages and blading. Associated with smaller passages and blading is an increased surface area that can cause decreased component efficiency related to frictional losses. Also associated with smaller passages and blading are losses related to increased blade tip leakages due to proportionately larger tip clearances. Therefore, all or a portion of the theoretical improvement and cycle efficiency attributed to the increase in the pressure ratio may be negated by the decrease in component efficiency. Current material limitations and cooling techniques for aircraft gas turbine engines have been inadequate to accommodate significantly increased operating temperatures, thus, inhibiting any significant working fluid temperature increase in the gas turbine.
Suitably designed wave rotors can function like key portions of conventional gas turbine engines to extract useful work by compressing and expanding the working fluid. However, unlike the conventional gas turbine engine that utilizes rotating airfoils, the transfer and extraction of energy in a wave rotor involves unsteady transient waves and flow processes. The wave rotor used in a cycle topping role allows an increase in the engine pressure ratio without suffering high losses. Simultaneously, the combustor exit temperature can be increased while using present material technology because the wave rotor has a self cooling feature occurring within it's passageways. The self cooling feature utilizes intermittently exposing individual passageway walls of the wave rotor to alternating elevated and reduced temperature gas flows, so that the thermal capacitance of the passageway walls can hold the average material temperature to an acceptable level.
Although prior wave rotors and methods of using transient gas flows are steps in the right direction, the need for additional improvements still remains. The present invention satisfies this need in a novel and unobvious way.